1. Field of the Invention
The invention is directed to a vibration damper of the type wherein a piston rod moveable in a cylinder has a first piston mounted stationary thereon and a second piston axially displaceable on the piston rod against a spring force. The cylinder includes a piston rod side work space, a work space remote from the piston rod and a work space between the two pistons. The pistons are provided with valves for connecting the work spaces.
2. Description of the Related Art
DE-OS 22 30 975 discloses a vibration damper for motor vehicles which has a first stationary piston at a hollow piston rod and a second piston which is displaceable axially against a spring force. The two pistons have through-openings which are outfitted with check valves. The damping force of the vibration damper is generated by a central, double-action damping valve inside the piston rod. The check valves in the pistons serve only to provide damping medium to a work space between the two pistons when the second piston executes an axial movement and the piston distance and, therefore, said work space change.
DE 39 39 650 C2 discloses a hydraulic damper arrangement in which a piston is fastened in an axially springing manner to a piston rod. The piston rod is fastened at the wheel side and the cylinder of the damper arrangement is fastened on the body side, so that the piston can act as a damper. A problem in a damper arrangement of this kind consists in that clearly audible operating noises occur.
It is the object of the present invention to provide a vibration damper which offers advantages with respect to comfort compared to a conventional vibration damper during high-frequency excitations.
According to the invention, this object is met in that in a first embodiment the second piston has at least one restoring spring or return spring on both sides and the piston is mounted so as to be displaceable axially in two directions against the return springs.
Compared to the prior art mentioned above, a reduction in damping force can be achieved for the moving in direction and for the moving out direction of the piston rod, so that a noticeable increase in comfort can be achieved.
In an alternate version, a second and third axially displaceable piston are associated with the stationary piston, wherein the second and third piston are pretensioned in their normal position by at least one return spring.
The advantage of the second solution compared with the first consists in that the spring rates of the return springs are not cumulative and accordingly the possibilities for optimal design of the damper force characteristics of the vibration damper are further improved.
It is provided that the through-openings in the pistons for both through-flow directions are outfitted with damping valves. The great advantage to this consists in that a hollow piston rod for a damping valve can be dispensed with. The piston which is stationary relative to the piston rod provides for basic damping with its damping valves. The additional damping of the axially movable piston is superimposed cumulatively on this basic damping.
In another advantageous construction, a damping force adjuster controls the effective cross section of at least one through-opening depending on the instantaneous position of the movable piston. With a damping force adjuster of this type, an effect like that of a rebound stop or compression stop can be achieved for the piston rod regardless of the stroke position of the piston rod.
In this connection, the through-openings controlled by the damping force adjuster have valve disks which at least partially cover the through-openings in their basic position, wherein the damping force adjuster controls the valve disk movement proceeding from a defined piston position of the movable piston.
Accordingly, it is provided that the damping force adjuster is constructed as a stop which is stationary relative to the piston rod.
The stop is formed by a spring plate for a return spring so that the fewest possible structural component parts are needed for the pistons. Insofar as the first piston has a supporting disk for at least one valve disk, this supporting disk can form the spring plate for a return spring of the second piston.
At least one of the spring plates on which the return springs are supported is mounted so as to be axially movable so that the return springs can be adapted to different damping force characteristics in the simplest manner possible.
In addition, a hydraulic end stop can be provided for the piston rod movement in that the vibration damper has a stop spring which enters into an operative connection with the axially movable spring plate proceeding from a defined or predetermined stroke position of the piston rod.
When the vibration damper is designed for good suppression of rolling, the damping action of a damping valve on or associated with the moving or second piston and the return spring which is associated with the through-flow direction of the damping valve are adapted to one another in such a way that the movable piston is still mounted in a springing manner even with damping force above a defined piston rod movement speed.
It can also be provided in addition that the piston rod of the vibration damper is connected on the wheel side and the cylinder is connected on the body side and the movable piston is dimensioned as an added mass. The movable piston damps in a frequency-dependent manner, whereas the first piston ensures that no damping noises occur.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.